Isolation of two molecular weight variants of the mouse growth hormone receptor

GH receptors (GHRs) have been shown by affinity cross-linking to be present in late pregnant mouse liver microsomes in three forms with cross-linked mol wts of 125,000, 62,000, and 56,000. The two lower mol wt forms of the receptor were partially purified by bovine GH-affinity chromatography of 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate-solubilized extracts of late pregnant mouse hepatic microsomes. The GHRs were identified from the partially purified receptor preparation and isolated by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The isolated GHRs had mol wts of 40,700 and 37,500, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Enzymatic cleavage of N-linked glycosylation from the isolated GHRs reduced their apparent mol wts to 33,600 and 30,900, respectively. Sixteen of the amino-terminal 17 amino acid residues of the two isolated receptors were sequenced and determined to be identical. One amino acid residue in each of the proteins, at position 14, could not be identified. Rabbit polyclonal antiserum was produced against the isolated GHRs. The resulting antiserum precipitated the isolated 40,700 and 37,500 mol wt proteins as well as cross-linked mouse GHRs (including the high mol wt form of the receptor). However, the antiserum did not inhibit the binding of mouse GH to either membrane bound or 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate-solubilized GHRs.